To David Thompson—who died blind, penniless, and bypassed by history—we owe our first knowledge of the American continent’s rugged Northwest

David Thompson was a short, stocky man with snub nose and hair “cut square” across his forehead in a way that made him resemble John Bunyan. That is all we know about his looks. Until recently, historians knew little about who David Thompson was or what he did, and even today, few people recognize his name. Among those familiar with his exploits, however, he is now deemed one of the most important explorers of the New World, and has been acclaimed as one of the greatest land geographers ever produced by the English-speaking people.

That is high praise, but consider Thompson’s achievements. During a twenty-year period, betweeen 1792 and 1812, he crossed and recrossed the unknown wilderness of the northwestern United States and Canada, usually accompanied only by Indians, exploring and mapping the principal features of more than a million and a half square miles of territory, from Hudson Bay to the Pacific Ocean and from the Great Lakes to the Athabaska wasteland of northern Canada. On the maps, when he began his explorations, all that vast region was a blank.

He was the first white man to explore and settle upon the upper Columbia River. He was the first to build white establishments in the present-day states of Montana, Idaho, and Washington. He was the first to make a full survey of the shore line of Lake Superior, and the first to map the relationship between the Missouri River and the principal streams of the central Canadian plains.

In addition, he was the first, and in some cases the only man to gather certain information that is today recognized as indispensable for an accurate history of the early West. He met Blackfeet and other Indians of the plains and Rocky Mountains who told him what it was like when they first got guns, and when they saw their first horse. He heard anecdotes and learned the history of Indian warfare and tribal movements before white men knew of the existence of those tribes. And in the American Northwest, his records have startled historians with references to other white men who were in that remote part of the continent at the same time as Lewis and Clark, including a mysterious second United States exploring expedition about which nothing else has ever been known.

Thompson’s discoveries and surveys enriched the world with knowledge of the northwestern part of this continent. But the professional cartographers and engravers who used his information failed to acknowledge him as their source, and the people who in later years followed the routes he pioneered were unaware that he was the author of the maps they used. Similarly, his written records were not published, and no one knew where he had been or what he had done. When he died in 1857—poor, blind, and unknown—he was buried in an unmarked grave in Montreal.

Thompson might have been altogether forgotten had it not been for the curiosity of a Canadian geologist, Dr. Joseph R. Tyrrell, who was working in the West during the 1880’s as a member of the Geological Survey of Canada. Tyrrell was struck by the completeness and accuracy of the old government maps he was using, and he became interested in trying to discover their source. His search led to the files of the Crown Lands Department of the Province of Ontario at Toronto, where he uncovered a group of weathered journals and notebooks of David Thompson, as well as a huge manuscript map of the western half of North America between the latitudes of 45 and 60 degrees, which the explorer had made years before. Study of the diaries and notebooks revealed the hitherto unsuspected extent of Thompson’s many journeys as a fur trader and surveyor for the Hudson’s Bay and the North West companies, and the map confirmed him as the original source for the government charts of the West that Tyrrell had been using.

In the years that followed, Dr. Tyrrell continued his quest for further information, and eventually learned that while Thompson had been in the service of the fur companies, his maps and reports had been sent by his superiors to Aaron Arrowsmith, the English cartographer, who used them to help prepare his maps of North America. But Arrowsmith never acknowledged Thompson as the source of his information. Dr. Tyrrell also learned that in 1814, while still in the employ of the North West Company, Thompson had completed his own great manuscript map of all the territory he had explored and surveyed. For a while it had hung in the dining hall of the company’s post at Fort William, on Lake Superior, where it was seen only by company partners and employees. At the time, the company had no interest in having the map circulated, because its members were then engaged in intense competition with the Hudson’s Bay Company, whose traders would have valued the detailed information it contained.